1. Field of the Invention
The present invention relates generally to a fault recovery system. More specifically, the invention relates to a fault recovery system and a transmission path autonomic switching system for setting a path bypassing failure upon occurrence of failure in connection used in a connection oriented network using a protocol establishing line connection using a source routing system performing path calculation on the basis of a topological information exchanged between nodes.
2. Description of the Related Art
In the conventional connection restoring system using an ATM (asynchronous transfer mode) network of this kind, a concentrated management system unitarily managing network topology is provided so that the concentrated managing system collects network topology information from all of nodes for preliminarily calculating an auxiliary path for the purpose of lower delay in recovery of connection upon occurrence of failure.
In this condition, the concentrated management system employs a system for preliminarily setting the auxiliary path for a currently used connection upon setting of a certain connection, and transmitting a control signal for switching connection at respective nodes upon occurrence of failure.
On the other hand, the concentrated management system may also employ a system, in which a path calculation is performed for bypassing failure at the occurrence of failure without preliminarily setting the auxiliary path to establish a connection bypassing the failure.
In the foregoing construction of the network, the concentrated management system may manage topology information of the network. Therefore, the auxiliary path for the currently used path can be determined.
On the other hand, a technology not relying on the concentrated control system has been disclosed in Japanese Unexamined Patent Publication No. Heisei 4-65942, for example. In the disclosed system, each node has a plurality of predetermined auxiliary paths and normally monitors conditions of the auxiliary paths, and selects an appropriate path in predetermined condition upon occurrence of failure.
On the other hand, according to a system disclosed in Japanese Unexamined Patent Publication No. Heisei 6-62001, for example, a control frame is generated upon occurrence of failure to transmit the control frame for all of the connected paths so that the auxiliary path is determined by the node receiving the control frame.
On the other hand, by a system disclosed in Japanese Unexamined Patent Publication No. Heisei 7-115420, for all of nodes from a node connected to a calling terminal, a connection for management separate from a connection for a user is preliminarily set to recover the connection for management in autonomic discrete manner upon occurrence of failure, and then connection is switched by connecting network topology information utilizing management connection.
Furthermore, in a PNNI (Private Network-Network Interface) protocol in an ATM (asynchronous Transfer Mode) forum provision as the background art of the present invention, routing means for autonomously exchanging network topology information in respective nodes, and signaling means for setting connection to dynamically perform source routing in path determination, are defined. Upon occurrence of failure, faulty connection is maintained as cut off.
Among connection recovery system in the conventional ATM network set forth above, in a method unitarily managing network topology, when a failure is caused in the corresponding bypass path during actual use of the network, it becomes necessary to calculate other replacement path to require substantial period in large amount of calculation to cause a problem to require long period in processing information.
The reason is that the bypass paths for all of combinations have to be calculated to make algorithm complicate. On the other hand, since concentrated management is required, various information becomes large amount to require long period for processing.
On the other hand, in the system disclosed in the foregoing Japanese Unexamined Patent Publication No. Heisei 4-65942, it becomes necessary to set a plurality of auxiliary paths preliminarily. Thus, when a network construction is modified, large amount of process is required in updating process of the preliminary paths.
The reason is that when variation is caused in the network construction, variation may be caused in database of the auxiliary paths owned by all of nodes forming the network.
On the other hand, in the system disclosed in Japanese Unexamined Patent Publication No. Heisei 6-62001, upon performing switching process, overall network can be influenced.
The reason is that a particular control frame for path retrieval is generated and transmitted to all of paths due to occurrence of failure. Therefore, traffic of the control packet is inherently increased depending upon scale of the network.
On the other hand, in the method disclosed in Japanese Unexamined Patent Publication No. Heisei 7-115420, it becomes necessary for setting management connection between all of nodes. Upon occurrence of failure, relatively long period is taken in switching.
The reason is that management connection is required for exchanging network topology information and a procedure for at first recovering management connection at the occurrence of failure is required.
On the other hand, in a specification of a current ATM forum, when failure is caused, it becomes necessary to re-establish connection by superior application or the like without recovering connection. On the other hand, when failure is caused while connection is established with a plurality of Any Cast terminals providing certain predetermined services, it is frequently required to receive services from the beginning.
The reason is that, in the former case, means for recovering failure is not provided, and in the later case, since the service can be received by establishing with any Any Cast terminal, it is possible to establish connection with the Any Cast terminal different from the Any Cast terminal connected precedingly.
In the foregoing conventional fault recovery system in the ATM network, since switching is performed for connection in point-to-point connection, it is not possible to recover point-to-multi points connection.
The reason is that multi points connection is not considered. Namely, even though one connection can be recovered, a plurality of connections cannot be recovered.
Also, in the conventional connection switching system, in switching to be performed in response to occurrence of failure, even if good quality of path can be obtained in the bypassing path, if the quality demanded by the user upon setting of connection is minimum quality, the path is inherently used at the minimum quality even after switching. Conversely, when quality before switching is good, the same quality of connection is retrieved after switching to narrow path selection to lower probability of retrieval of the bypassing path.
The reason is that when failure is caused, recovery is attempted to establish bypass connection in the same quality as that in the preceding connection.
On the other hand, the conventional connection switching device performs switching at the occurrence of failure. When the quality demanded by the user upon establishing connection is the minimum quality in a range of quality, the user has to perform communication in the same quality until connection is shut off.
The reason is that there is not means for modifying the quality once demanded by the user within a possible range of quality until the current connection is shut off. At this time, since the quality of connection falls within a demanded range, it is not regarded that failure is caused. Thus, switching is not performed.